This invention relates generally to power compensation circuits, and more specifically to a method and apparatus for supplying a controlled clock pulse to driving circuitry to provide constant power to a fastening solenoid regardless of fluctuations in power line voltage.
It has been recognized for some time that typical B 115 VAC lines often fluctuate in voltage. Unfortunately, such fluctuations may also provide equally fluctuating power to certain electrical devices resulting in decreased efficiency, poor performance, damage to the device and other detrimental effects. Although devices which perform voltage compensation such as voltage clipping devices do exist in the art, such devices suffer in that they do not provide controlled power to devices which do not represent purely resistive loads.
A further deficiency of prior art devices is a failure to provide a controlled amount of power for a relatively short predetermined amount of time to an electrical device such as an engaging solenoid of an electric fastening machine in view of power line fluctuations. More specifically, electric fastening machines generally include a fastening solenoid which is provided with a pulse of short duration to engage the solenoid and therefore fasten material. As a result, devices have been provided which produce a pulse comprising a portion of the positive half of the AC line voltage sine wave. More particularly, device SW-197.2 manufactured by Swingline Inc. will provide a pulse of the 115 VAC line to the engaging solenoid, said pulse starting when a digital counter reaches its sixteenth count after the 115 VAC sinusoidal wave reaches a positive going zero crossing. This pulse has a magnitude approximately equal to or proportional to the corresponding portion of the sine wave. This pulse may exist for a duration corresponding to, illustratively, 70.degree. to 110.degree. of the 115 VAC line, where the positive going zero crossing represents 0.degree.. However, since the 16 bit counter is driven by a clock of constant frequency, this firing pulse will exist from 70.degree. to 110.degree. regardless of the magnitude of the input line voltage. An increase in line voltage magnitude will provide a pulse from 70.degree. to 110.degree., but at a higher voltage and therefore increased power. Such a pulse of increased power may result in the engaging solenoid engaging in too forceful a manner or short circuiting from overload. Similarly, a decrease in line voltage magnitude will provide a pulse from 70.degree. to 110.degree. but at a lower voltage. Such a pulse of decreased power may result in a supply of inadequate power to the engaging solenoid, resulting in jamming or insufficiently fastened materials.